Im planning to build a core 2 quad Q6600/Q9450@P35 MB,2gb ram,8800GTS 512,2 x 500GB HDD@RAID,2 DVD-RW.
Im looking to overclock the CPU to about 3.6Ghz and also overclock the 8800gts to its max the ram would be running at about 800-900mhz.so how much power do i need for this system?would 500W be enough @ peak usage?thx in advance

I think 500 is cutting it too close.  I ran your spec'd system through the eXtreme Power Calculator and came up with 465Watts. Data used:
High End Desktop / 85% TDP / Q9450 @ 3.5Ghz Vcore 1.4 / 2GB DDR2 @ Stock
8800GTS G92 512MN @ Stock/ 2 SATA HD / 2 DVD+RW / 3 USB devices
3 120mm case fans (2LEDs) / 90% system load / 20% capacitor aging

Throw in the CPU cooler fan, the GPU overclock, possible future upgrades to 4GB RAM, maybe a Blu-Ray drive, another HD and a few other items and I'd suggest going with a good PSU in the 600Watt range.

Something along the lines of a Corsair HX520 or similar would be more than sufficient, just make sure it's a quality 500 watt unit not a crappy Rosewill type.

/\ agreed. Just make sure you get something a little over 500W, Corsair HX 520W or the OCZ GameXstream 600W should be enough.

Here is what result i got from the wattage calculator.thanks to WR2 what amp@12V would you recommend?
 
System Type:  Single Processor  
Motherboard:  High End - Desktop  
CPU:  Intel Core 2 Quad Q6600 G0 2400 MHz Kentsfield  
Overclocked:  3600 MHz, 1.5 V  
CPU Utilization (TDP):  100% TDP  
     
RAM:  2 Sticks DDR2 SDRAM  
Video Card:  NVIDIA GeForce 8800 GTS 512MB  
Video Type:  Single Card  
     
SATA HDD:  2 HDDs  
     
DVD-RW/DVD+RW Drive:  2 Drives  
     
USB:  3 Devices  
Front Bay Card Reader:  Yes  
     
Fans    
LED:   3 Fans 120mm;  2 Fans 250mm;  
     
Keyboard and mouse:  Yes  
     
System Load:  100 %  
     
Capacitor Aging (+ W %):  15 %  
     
 
   
Recommended Wattage:  607 Watts

First off I don't think that the CPU will hit a voltage of 1.5V thats maybe a little too much. Another thing you won't hit CPU Utilization (TDP):  100% TDP.

Corsair 620HX = job done. That wattage calculator a) overestimates & b)is sponsored by companies that want you to buy overpriced, overpowered PSU's.

 
The Enermax Infiniti 720W will give you a little more room to grow, its modular as well.
 
ENERMAX INFINITI EIN720AWT ATX12V/ EPS12V 720W Power Supply 100 - 240 V RoHS - Retail  
http://www.newegg.com/Product/Prod [...] 6817194021

alright.but what amps am i looking at?

 
Any good quality PSU you get should have enough or plenty of amps to run you're system fairly well.

The PSU calculator takes a SWAG at the size of PSU and not the actual power draw of an proposed system.
It's true the PSU calculator overestimates a bit, but on the other hand people tend to underestimate how much stuff they'll end up wanting to run off the PSU.  A 3rd HD, another 2GB RAM, a Firewire camera or a couple more USB devices, maybe a TV tuner card and a Blu-Ray drive or a NextGen GPU, etc.  

I couldnt find anything about what a max OC'd 8800GTS/G92 draws. I'd suggest 50amps +12volts is in the ballpark - more than you'd need now, probably enough for modest upgrading.  But if you think you'd want to load up your system a bit more like what I mentioned above it wouldnt hurt to look for 60amps.
Corsair 620HX = 50Amps  $145 after rebate
Enermax Infiniti 720W = 56Amps $170 after rebate
PC P&C  Silencer 750 = 60Amps  $170 no rebate & free shipping
OCZ GameXStream 700 = 50Amps $100 after rebate
Corsair 750TX = 60Amps $150 after rebate

i

 
Nowhere near close. 2 8800GT's + 5 HDD's + 5 case fans + 90nm 939 x2 CPU + 4 USB devices + DVD/RW does not even come close to putting a 620HX under load, so a single 8800GTS is going to be nowhere near 50 amps, sheesh.

50amp on OC 8800gts?are you sure its this much?i dont think a single rail provide that much of amp.

$65 shipped after $15 rebate and will easily power any non-SLi setup:
http://www.buy.com/prod/corsair-vx [...] 52646.html
 

Nice.

I never said a 8800GTS would draw 50amps. I only said I couldnt find its draw at max OC.
A 8800GTS/G92 only takes ~120watts at full load @ stock or 10amps.  A max OC? Take a guess.
Q9450 95watts at stock.  TDP is 130watts and thats about what you get from a Q9450 @ 3.6Ghz 1.3vcore from the eXtreme Power Calculator.  Thats about 12.5amps.  Maybe 25amps total for just the OC'd CPU/GPU?

50Amps is what I recommended for total +12volts.  And I did say it was more than you'd need with the items you listed.  Which is what mousemonkey's 620HX has - 50amps total +12.

edit; with 75watts through the PCI-e slot and 75 watts available through the PCI-e connectors the max you can provide to the 8800GTS is 150watts or 12.5amps.
3870X2 takes 188watts under load @ stock which is why it has the PCI-e x6 and PCI-e x8 connector power slots.  15.5Amps @ stock.  

50Amps of +12volts has to be pretty close - its what you recommended to the OP with the Corsair 620HX.

My apologies, I missed the full stop and assumed you were referring to just the GPU not the total system.